1. Field of the Invention
The present invention relates to a resin film to be used for connecting electronic parts, and a method for connecting electronic parts based on the use thereof, more particularly to a resin film suitable for electrically and mechanically connecting an electronic part such as a semiconductor chip and another electronic part such as a substrate, and a method based on the use thereof.
2. Description of the Prior Art
In recent years, with the development of small and thin electronic parts, a demand has been rising for the connection of a minute part such as a semiconductor chip with a substrate carrying a microcircuit pattern, and with such tendency, the interval between adjacent wires becomes increasingly short.
Conventionally, for such purpose, a method has been principally employed whereby a wire is bonded between the connection terminals of parts to be connected. However, an alternative method whereby parts to be connected are allowed to face to each other and then bonded directly together is more suitable than the conventional bonding method for the quicker production of small and thin parts, and thus the latter method, or the flip-chip connection is more avidly employed nowadays. The connection joints of parts joined by this method are mainly sealed by a cheap resin for the protection of the joints from the environmental adverse effects and for the insurance of stable connection operation of the joints. For the sealing, a method has been employed whereby terminals are allowed to face to each other, they are connected electrically and then a liquid resin is poured into the gap between the terminals. Connection of connection terminals is achieved by soldering, pressure contact of gold-to-gold terminals, and bonding with an electroconductive paste.
However, with the development of smaller and thinner parts, the gap between a substrate and the part placed opposite thereto, and the distance between adjacent terminals of part become smaller, which makes difficult the pouring of a liquid resin (so-called under-fill) into or through those gaps and intervals. Generally, a thermosetting resin with a low viscosity such as an epoxy resin is used.
Another alternative method has been proposed (Japanese Patent Laid-Open Publication No. 2-7180) whereby a liquid resin is applied in advance onto a part of a substrate which will carry a chip before the substrate and chip are assembled; the terminals to be connected are placed opposite properly to each other; they are pressed together while being heated; and thus electrical as well as mechanical connection is established between the two terminals (dispensing with the use of an under-fill). With this method, the semiconductor chip and the substrate are connected to each other electrically because their terminals come into direct contact to each other owing to a contraction force accompanying the hardening of thermosetting resin. Generally, when an electronic part is used in a high-temperature environment, or a semiconductor element generating a high temperature such as a power module is incorporated in a semiconductor chip, resin around that semiconductor chip expands in the presence of heat, and contracts after use as the high temperature subsides. Repeating this process will lead to the deterioration of the resin in question.
With the above method, electric connection of terminals is maintained only by the contraction force of resin generated after hardening which is applied around the terminals in question. Therefore, with the deterioration of resin after repeated expansions and contractions, the contraction force thereof becomes slackened, and as a result of this, when the thermal expansion in the presence of heat exceeds the contraction after withdrawal of heat, failure of electrical connection results. To prevent this, it is necessary to reduce the thermal expansion coefficient of the resin to maintain the thermal expansion thereof at a low level. For this purpose, as shown in FIG. 1, for electrical connection of a semiconductor chip with a substrate, a resin 111 is used which contains inorganic particles 112 having a smaller thermal expansion coefficient such as silica particles.
In this case, when the connection terminal of a semiconductor chip has a tip having essentially a flat surface, a liquid resin may creep between the opposing terminals of semiconductor chip and substrate, which may lead to failed electric connection between them. Particularly, inorganic particles such as silica particles contained in the resin easily creep between such opposing terminals. As a preventive measure for this, a method has been proposed (Japanese Patent Laid-Open Publication No. 9-97816) whereby a pointed metal projection (bump) is prepared on the connection terminal of a semiconductor chip.
Or a further alternative method or the connection method based on the use of an anisotropic resin has been proposed (Japanese Patent Laid-Open Publications Nos. 62-141083 and 7-157720) whereby, as shown in FIG. 2, conductive particles 122 are allowed to uniformly disperse in a resin 121 interposed between a semiconductor chip and a substrate, and thus to exist between the opposing terminals, and then the terminals are pressed together while being heated thereby establishing electric connection of those terminals as well as ensuring insulation from adjacent terminals. In this method, for conductive particles 122, for example, metal particles made of nickel or a soldering alloy, or resin particles whose insulating surfaces are plated with gold are used. To prepare such resin particles, a resin in the form of a liquid (or paste) or a film is used. In this method, terminals to be connected should preferably have a flat surface because then conductive particles are more effectively maintained between the opposing connecting terminals.
As discussed above, when a liquid (paste) resin having a thermosetting property is used as a resin for flip-chip connection, the resin requires a long time lasting several minutes to several hours before it hardens, which will lead to the lowering of productivity.
Alternatively, as shown in FIG. 3, when the connection terminal 136 of a semiconductor chip 135 is allowed to have a bump 139 thereupon, and is pressed against a substrate 137 while being heated, the resin 131, particularly small-sized inorganic particles 133 contained therein, when they have a broad distribution in particle size, may be trapped in the space between the connection terminal 138 of substrate 137 and the bump 139, which may cause troubles leading to incomplete electric connection of involved terminals.
A resin with a low stress developing property has been favorably employed regardless of whether it is used in connection with conductive particles or not, because such a resin improves the reliability of terminal connection, particularly resistance of connected terminals against thermal shocks. However, when a resin contains inorganic particles, it becomes hard, and thus its affinity at interfaces to the electronic part tends to fall. When an anisotropic, conductive resin is used, usually it is never provided, or provided only with a comparatively small amount of inorganic particles. Therefore, such a resin will have a rather high thermal expansion coefficient, and thus its resistance to heat stresses and moisture may be insufficient.
A first object of this invention is to provide a resin film which, when used for the seal of connection between a semiconductor chip and a substrate, is highly affinitive to the chip and substrate at interfaces, and will give less adverse effects to the connection terminals even under thermal stresses after setting, and a method based on the use of such a resin film for the electric connection of electronic parts.
A second object of this invention is to provide a resin film which, being suitably used for the seal of connection achieved by the flip-chip method, can seal such a connection in a short time, and ensure high reliability of the connection, and a method based on the use of such a resin film for the electric connection of electronic parts.
A third object of this invention is to provide a resin film made of a resin containing inorganic particles which, even when the particles are trapped in the space between a semiconductor chip and a substrate, is so prepared that the reliability of connection may not be impaired, and a method based on the use of such a resin film for the electric connection of electronic parts.